From H. H. Wieder, Hall Generators and Magnetoresistors, Pion Limited London 1971, page 86, there is known an apparatus for the measurement of electrical power, including a Hall generator serving as a multiplier, which receives on an input thereof an electrical signal proportional to the voltage component of the electrical power, and which is subjected to an external magnetic field proportional to the current component of the electrical power. The external magnetic field is coupled to the Hall generator through a magnetic core. From pages 74 and 77 of the above-noted reference, a multiplier is also known, which consists of either two voltage sources or resistors, on one hand, and two magnetoresistors on the other hand, connected so as to form a bridge circuit.
In Hall generators and magnetoresistors a galvanomagnetic effect in semiconductors is exploited. A magnetic field to be measured is coupled at a right angles to the main plane of a plate-shaped semiconductor, which is only possible at an adequate efficiency by means of a magnetic core, in a view of the well known low sensitivity of the Hall generators or the magnetoresistors. The considerable dependence on temperature, and poor linearity is a disadvantage of this circuit.
There is further known a current detector for the measurement of a current to be measured in a conductor from the IEEE transactions on magnetics, November 1976 pages 813-815, in which four ferromagnetic magnetoresistor thin film pairs form a bridge. The thin films of each pair are magnetostatically coupled to one another, so that a current flowing in one thin film generates an auxiliary magnetic field in the other thin film. The magnetic external field generated by the current to be measured magnetizes the thin films in the direction of their hard axes. As the intensity of the auxiliary magnetic field depends on the magnitude of the current feeding the bridge, this current detector cannot be used as a multiplier.